1. Field of the Invention
The present invention relates to a fuel cap which is installed to a filler neck of a fuel tank in automobiles.
2. Description of the Prior Art
In a fuel cap 1 of the prior art as shown in FIG. 1, a cap body 2 of cylindrical shape is provided on upper side with a flange member 5 which is projected outward in the radial direction of the cap body 2, and a cover 9 which covers the upper side of the cap body 2 is externally fitted to the flange member 5 (refer to U.S. Pat. No. 4,177,931).
A male screw portion 2a which installs the fuel cap 1 to a filler neck 10 is formed on outer circumference of the cap body 2, and a seal ring 4 which seals the filler neck 10 at the installing state to the filler neck 10 is arranged on lower surface of the flange member 5.
V-like grooves 6, 7 with V-like cross-section are formed on the upper and lower surfaces of the flange member 5 at outward position from the seal ring 4 in the radial direction of the cap body 2 along the circumferential direction of the cap body 2, and a weak portion 8 with small thickness is formed by these V-like grooves 6, 7.
The weak portion 8 is provided so that the flange member 5 can be separated from the cap body 2 in order to secure the seal property with the filler neck 10, when the external force, i.e. force applied to the fuel cap 1 so as to force open the fueld cap 1 from the filler neck 10, acts on the flange member 5 through the cover 9 by a body outside plate or the like (not shown) after the fuel cap 1 is installed to the filler neck 10.
Numeral 3 designates a valve mechanism which adjusts pressure within the fuel tank after the fuel cap 1 is installed to the filler neck 10.
In the fuel cap 1 of the prior art, the weak portion 8 which separates the flange member 5 from the cap body 2 at the prescribed time is formed by the V-like grooves 6, 7 provided on the upper and lower surfaces of the flange member 5 respectively in one groove per each surface.
Consequently, when the flange member 5 is separated, one surface connecting the most depressed portions of the V-like grooves 6, 7 always becomes the breaking surface D, and the weak portion 8 is broken at the breaking surface D and the separation is performed.
In such breaking, however, the breaking load to the external force F1 acting nearly parallel to the breaking surface D becomes small, and the breaking load to the external force F2 acting nearly perpendicular to the breaking surface D becomes large. Consequently, in the fuel cap 1 of the prior art, the breaking surface D is one sort, and the breaking load of the weak portion 8 is varied by the direction of the external force acting on the flange member 5.